|Trade names||Generic; many brand names worldwide|
|Oral, intravenous, intramuscular|
|ATC code||M03BC01 (WHO) N04AB02 (WHO)|
|Biological half-life||13-20 hours|
|Excretion||Renal and biliary|
|Chemical and physical data|
|Molar mass||269.381 g/mol|
|3D model (Jmol)||Interactive image|
Orphenadrine (sold under many brand names worldwide) is an anticholinergic drug of the ethanolamine antihistamine class; it is closely related to diphenhydramine. It is used to treat muscle pain and to help with motor control in Parkinson's disease, but has largely been superseded by newer drugs. It was discovered and developed in the 1940s.
Orphenadrine is used to relieve pain caused by muscle injuries like strains and sprains in combination with rest and physical therapy. A 2004 review found little clinical evidence for the safety or efficacy of orphenadrine for this use.
Orphenadrine and other muscle relaxants are sometimes used to treat pain arising from rheumatoid arthritis but there is no evidence they are effective for that purpose.
A 2003 Cochrane Review of the use of anticholinergic drugs to improve motor function in Parkinson's disease found that as a class, the drugs are useful for that purpose; it identified one single-site randomised, cross-over study of orphenadrine vs placebo. Orphenadrine and other anticholinergics have largely been superseded by other drugs; they have a use in alleviating motor function symptoms, and appear to help about 20% of people with Parkinson's.
Orphenadrine has the side effects of the other common antihistamines in large part. Stimulation is somewhat more common than with other related antihistamines, and is especially common in the elderly. Common side effects include dry mouth, dizziness, drowsiness, upset stomach or vomiting, constipation, urine retention, blurred vision, and headache. Its use in Parkinson's is especially limited by these factors.
People with glaucoma, digestive problems like peptic ulcers or bowel obstruction, or sphincter relaxation disorders, or with enlarged prostate, bladder problems, or myasthenia gravis, should not take this drug.
Orphenadrine is known to have this pharmacology:
- Nonselective mACh receptor antagonist (anticholinergic, 58% as potent as atropine)
- H1 receptor antagonist (antihistamine)
- NMDA receptor antagonist (Ki-value of 6.0 +/- 0.7 μM, one third as potent as phencyclidine, which binds with a Ki of 2 μM)
- NET blocker (norepinephrine reuptake inhibitor)
- Nav1.7, Nav1.8, and Nav1.9 sodium channel blocker
- HERG potassium channel blocker
Orphenadrine has been available as a citrate salt and a hydrochloride salt; in the US as of February 2016 the citrate form was available in tablets, extended release tablets, and by injection for acute use in a hospital setting.
George Rieveschl was a professor of chemistry at the University of Cincinnati and led a research program working on antihistamines. In 1943, one of his students, Fred Huber, synthesized diphenhydramine. Rieveschl worked with Parke-Davis to test the compound, and the company licensed the patent from him. In 1947 Parke-Davis hired him as their Director of Research. While he was there, he led the development of orphenadrine, an analog of diphenhydramine.
Prior to the development of amantadine in the late 1960s and then other drugs, anticholinergics like orphenadrine were the mainstay of Parkinson's treatment.
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